GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



175 



Issuing in the brain-cavity on the anterior slope of the petrosal (Plate L), the vessel follows a small 

 groove, at the bottom of the channel for the trigeminus, forward and inward, piercing the cerebral surface 

 of the basisphenoid and again issuing in a small foramen that is lateral to the sella turcica, immediately 

 thereafter uniting with the ophthalmic artery (Stehlin). The arteria promontorii is very small, and both 

 Tandler (p. 763) and Stehlin (p. 1207) found that in Jjernur the chief supply for the c('i'e])i'al arteries is 

 furnished by the vertebral arteries. 



Indrisin.e 

 Plates XLVI, XLIX, L; Text Fi-. (i7 



In a skull of Propithecus sp. (Amer. Mus. 31255) the foramina for the carotid are located as they are 

 in Lemur. The posterior carotid foramen on the posteroexternal corner of the bulla leads into a prominent 

 canal lying along the external face of the cochlea and no doubt carrying the arteria promontorii; the 



1 2 



Fig. 67. Norma basalis of the skull of two siil)fossil indrisine lenuirs from .Vmpasamljzimba, Madagascar. After 

 Standing. 



(1) Palceopropillirnis nin.vi iinis, one-half natural size. 



(2) Mesopropithccus pilhccoides, natural size. 



canal runs forward to the anteroexternal corner of the roof of the cavity of the bulla, pierces the basi- 

 sphenoid and enters the brain-cavity through a very small foramen that is lateral to the sella turcica. 

 The stapedial branch probably enters from the petrosal into the brain-cavity and follows the deep venous 

 sulcus that runs along the base of the brain-case at its outer margin, thence emerging into the orbit through 

 the prominent cranio-orbital foramen. The foramen lacerum iwsterius is divided into two distinct 

 openings as in Lemur. 



